Browsing by Author "Mäkelä, Ville"

With their ability to convert chemical energy to electrical energy through electrochemical reactions, rechargeable batteries are widely used to store energy in various applications such as electronic mobile equipment, aerospace aviation, road transportation, power grid, and national defense industry Numerous battery types are available commercially. Lithium ion-based batteries stand out due to several key advantages such as high operating voltage, high specific energy, and long cycle life. They also have a market dominance in a wide range of electric vehicles. However, like all battery technologies, lithium ion-based ones suffer from the effects of aging-induced degradation which can lead to reduced capacity, lifetime, and in some cases even safety hazards. One method of preventing/slowing down these aging reactions is to modify the standard battery materials by using dopants and additives. They are specific impurities purposely introduced into the battery during the manufacturing process. In this master’s thesis, the effect of additives (Mg/Al) on the aging of Li-ion cells was examined by using X-ray absorption spectroscopy, more specifically x-ray absorption near edge structure (XANES). For the experiment, 7 different cells, all containing lithium cobalt oxide as the major component (with 4 having a stoichiometric ration of Li/Co, and 3 being Li-rich), with 5 of them containing Mg/Al as dopants, and 2 containing no dopants were examined using XANES as a function of aging in terms of charge/discharge cycles. The dopants were introduced at different stages of the material preparation, either at the lithiation step or at the synthesis of the precursor. This thesis focuses on the XANES experiment and the data analysis, with extensive literature review on the topic of using additives and dopants. The cells were prepared by the Aalto University. The results showed that of the cells with dopant materials, the cells doped during lithiation stage aged slightly better after cycling than the undoped ones, whereas the cells doped during precursor stage aged worse than the undoped cells. This would suggest that doping might be more effective when done during the lithiation stage.